Nuclear Magnetic Resonance Microscopy Research Articles

High-Performance Materials Improve the Early Shrinkage, Early Cracking, Strength, Impermeability, and Microstructure of Manufactured Sand Concrete

The poor early shrinkage and cracking performances of manufactured sand concrete, waste powder concrete, and recycled aggregate concrete are the main difficulties in engineering applications. To solve these problems, early shrinkage and cracking, strength, and impermeability tests were performed on high-volume stone powder manufactured sand concrete mixed with fly ash and slag powder (FS), a shrinkage-reducing agent (SRA), polyvinyl alcohol (PVA) fibers, and a superabsorbent polymer (SAP). Furthermore, the microstructures and pore structures of these concretes were revealed using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results showed that the mixture of FS, SRA, PVA fibers, and SAP could effectively inhibit the shrinkage strain and cracking area of the concrete. The effect of the SAP on reducing the early shrinkage of the concrete is the greatest, and the shrinkage strain can be reduced by 76.49%. The PVA fibers had the most obvious effect on inhibiting the early cracking of the concrete, and the total cracking area was reduced by 66.91%. Significantly, the incorporation of the FS can improve the particle gradation and the pore structure and improve its compactness. The PVA fibers not only provide good carriers for cement-based materials but also enhance the bonding force between the particles inside the concrete, filling the pores inside the concrete, inhibiting the loss of water, and reducing the generation of internal microcracks. The FS and PVA can reduce the shrinkage and cracking risk and improve the strength and impermeability of the concrete. Although the SRA and SAP can reduce the shrinkage and cracking risks, it will lead to a significant decrease in the later strength and impermeability. The main reason is that the SRA leads to an increase in micropores in the matrix and microcracks near the aggregate, which are not conducive to the development of the strength and penetration resistance of the MS. Similarly, the SAP can promote the rapid formation of ettringite (Aft) at an early age and improve the early shrinkage, early cracking, and early strength of the concrete. However, with an increase in age, the residual pores, after SAP dehydration, will cause the deterioration of the concrete pore structure, resulting in the deterioration of the strength and impermeability.

Understanding the role of natural pozzolana in regulating the early hydration reaction process and microstructure of Portland cement

The present study examines the regulatory role of natural pozzolana (NP) on the early-age hydration process and microstructural development of Portland cement. Through a series of experiments, including low-field nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetric (TG) analysis and scanning electron microscopy (SEM), it was found that NP significantly influences the hydration kinetics and chemical shrinkage of cement paste. The addition of NP was shown to reduce the early-age chemical shrinkage and refine the microstructure by decreasing the quantity of harmful pores and increasing harmless pores, as evidenced by the bimodal distribution observed in pore size distribution (PSD) analysis. XRD and TG results indicate that NP reacts with calcium hydroxide to form additional calcium silicate hydrate (C-S-H) gel, thus improving the interfacial transition zone and resistance to carbonation. SEM micrographs further confirm the improved microstructure with fewer microcracks. The findings suggest that NP can be effectively utilized to optimize the early-age performance of concrete, offering a sustainable approach to improving its durability and long-term structural integrity.

Tracking the Dimensionality Transition from a Three Dimensional Single Crystal to a Two Dimensional Perovskite

AbstractThis work carefully studied the transition from 3D perovskite to 2D perovskite. Our system includes single crystals (SCs) of MAPbBr3, which were dipped in a solution of barrier molecules. Three monoammonium cations and one di‐ammonium cation were studied. Absorbance and cathodoluminescence were used to follow the formation of low‐dimensional perovskite on the SC surface. Quantitative nuclear magnetic resonance and scanning electron microscopy assist in quantitatively tracking the exchange process. We followed the barrier molecules′ concentration during the exchange process and their penetration depth into the 3D single crystal. The short aliphatic chain penetrates much farther into the crystal (ca. 450 μm) than the long aliphatic chain barrier molecule. In contrast, the process time is the opposite: the long aliphatic chain requires 5 days to achieve an equilibrium state compared with 15 days for the short aliphatic chain. Ab initio calculations indicate that the exchange process initiates due to the methylammonium vacancies on the surface, and the process is inhibited by the interactions between the −NH3 group and the PbBr2 planes. This work sheds light on the kinetics and thermodynamics of the transition from 3D to 2D perovskites, which is important for stabilizing the hybrid perovskites.

Mechanical Properties and Sulfate Freeze–Thaw Resistance of Calcium Carbonate Whisker-Reinforced Iron Ore Tailings Concrete

Iron ore tailings from iron ore mines pose environmental challenges. However, their reuse could provide significant environmental benefits. This study focused on producing clean concrete using iron ore tailings as crushed stone aggregate (IOTA) and calcium carbonate whiskers (CWs) as reinforcement. Five mixture groups were prepared: normal concrete (NAC) with natural crushed stone aggregate (NA), iron ore tailings concrete (TAC) with IOTA, and CW (10%, 20%, and 30%)-reinforced TAC (TAC-CW). Mechanical properties like the compressive strength (fcu) and splitting tensile strength (fst), as well as sulfate freeze–thaw (F-T) cycle resistance, were thoroughly investigated. Additionally, pore structure and microstructure were characterized using nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) techniques. The results showed that IOTA’s complete replacement of NA decreased concrete mechanical properties and frost resistance, but incorporating CWs effectively compensated for these losses. Specifically, the fcu and fst of TAC-CW20 with 20% CWs increased by 23.26% and 49.6% compared to TAC and were higher than those of NAC. With increasing F-T cycles, concrete internal pore structure significantly deteriorated, and corrosive products increased significantly, which was further confirmed by SEM. TAC-CW20 significantly optimized pore structure. Overall, the successful application of iron ore tailings as eco-friendly materials enhanced concrete performance and reduced the environmental impact of construction activities.

Microstructure and chloride transport of aeolian sand concrete under long-term natural immersion

Abstract River sand was consumed in large quantities, and alternatives to river sand were urgently needed. There are a large number of natural resources of aeolian sand in western China. Aeolian sand was prepared into aeolian sand concrete (ASC). It can greatly reduce the consumption of river sand and inhibit the process of desertification to protect the environment. ASC is a new type of concrete material prepared by using aeolian sand as fine aggregate. To clarify the chloride ion transport behaviour in the ASC under long-term natural immersion, the aeolian sand was 100% substituted for the river sand to prepare the full ASC with three water–binder ratios. The ASC was naturally immersed in 3 and 6% NaCl solutions for a long time, and nuclear magnetic resonance and microscopic scanning electron microscopy techniques were used. The change rule of chloride ion content at different depths of the ASC was studied, and its microstructure characteristics under different erosion times were analysed. The results showed that the free chloride ion concentration at different depths of the ASC increased with increasing water–binder ratio, immersion time, and chloride concentration. After soaking in the salt solution, the hydration products in the ASC reacted with chloride ions to form Friedel salt, which filled the internal pores and microcracks of the ASC, improved its interface transition zone structure, and increased the compactness of the test piece. The porosity of the three groups of ASC with different water–binder ratios decreased by 0.95, 1.03, and 1.15% after soaking in 6% salt solution for 12 m. To study the diffusion law of chloride ions in ASC, combined with influencing factors such as temperature, humidity, D value, deterioration effect and chloride ion combination, Fick’s second law was modified, and a chloride ion diffusion model of ASC with high accuracy was established, with a fitting correlation number above 0.93, which provided a reference for the research and application of ASC in saline areas.

Serum response factor promoting axonal regeneration by activating the Ras-Raf-Cofilin signaling pathway after the spinal cord injury.

Serum response factor (SRF) is important in muscle development, tissue repair, and neuronal regulation. This research aims to thoroughly examine the effects of SRF on spinal cord injury (SCI) and its ability to significantly impact the recovery and regeneration of neuronal axons. The researchers created rat models of SCI and scratch injury to primary spinal cord neurons to observe the expression of relevant factors after neuronal injury. We found that the SRF, Ras, Raf, and cofilin levels increased after injury and gradually returned to normal levels. Afterward, researchers gave rats with SCI an SRF inhibitor (CCG1423) and studied the effects with nuclear magnetic resonance and transmission electron microscopy. The SRF inhibitor rodents had worse spinal cord recovery and axon regrowth than the control group. And the apoptosis of primary neurons after scratch injury was significantly higher in the SRF inhibitor group. Additionally, the researchers utilized lentiviral transfection to modify the SRF expression in neurons. SRF overexpression increased neuron migration while silencing SRF decreased it. Finally, Western blotting and RT-PCR were conducted to examine the expression changes of related factors upon altering SRF expression. The results revealed SRF overexpression increased Ras, Raf, and cofilin expression. Silencing SRF decreased Ras, Raf, and Cofilin expression. Based on our research, the SRF promotes axonal regeneration by activating the "Ras-Raf-Cofilin" signaling pathway.

Fractal and Multifractal Characteristics on Pore Structure of Coal-Based Sedimentary Rocks Using Nuclear Magnetic Resonance

Summary Unconventional reservoirs have nanoscale pores, complex pore structures, and heterogeneity that directly affect reservoir storage performance and fluid transport capacity. In this study, shale, mudstone, and sandstone, three typical coal sedimentary rocks from the Daqiang coal mine in the Tifa Basin, were selected for nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) investigation, with the aim to investigate the pore structure and multifractal characteristics of the coal sedimentary reservoirs and to qualitatively analyze the effects of the physical property parameters and the mineralogical compositions on the multifractal parameters. The distribution data of the NMR T2 spectra were analyzed. The results showed that (1) SEM analysis concluded that the pore system of the three different lithological samples (mudstone, shale, and sandstone) was dominated by mineral matrix pores (i.e., intergranular and intragranular pores) and in the sandstone samples, there were only a few biological pores found. (2) The distribution of the NMR T2 spectrum peaks indicates that the sandstone and shale T2 spectra are bimodal, dominated by micropores, and contain a small number of transitional pores; most of the T2 spectra of mudstone are single peaks in distribution, mainly dominated by micropores. (3) Multifractal parameters are positively correlated with porosity and significantly negatively correlated with permeability; multifractal parameters are significantly positively correlated with the content of clay minerals and kaolinite, which suggests that the increase in clay minerals and kaolinite content enhances the heterogeneity of the pore space. The negative correlation with the content of quartz suggests that the enrichment of quartz reduces the irregularity of the pore space.

Experimental study on influencing mechanism of the multiple effect of steel slag powder for coarse tailings cemented backfill.

The gradation of aggregate and the hydration reaction of cementitious materials are important factors affecting the performance of backfill materials. Steel slag powder (SSP) can be used as both aggregate and cementitious material according to different particle size. SSP has multiple influencing effects on coarse tailings cemented backfill (CTCB). Experiment with different content SSP in the CTCB was designed. And uniaxial compression, nuclear magnetic resonance and scanning electron microscopy techniques were used to characterize its macro and micro characteristics. The relationship model of aggregate characteristics on strength and porosity was established by analyzing the characteristics of aggregate using gradation and fractal. The conclusions mainly include: (1) SSP plays three main roles in the CTCB: optimizing the gradation, generating hydration reaction and influencing the hydration reaction of cement. (2) There are good gradation and fractal characteristics between SSP and coarse tailings, with a grading index of 0.30-0.61 and a fractal dimension of 2.12-2.61. (3) The relationship between strength, porosity and gradation, fractal dimension was quadratic function relation, and then the grading index and fractal dimension for optimal strength and pore characteristics are 0.45-0.49 and 2.33-2.40 respectively.

Structural Analyses of Designed α-Helix and β-Sheet Peptide Nanofibers Using Solid-State Nuclear Magnetic Resonance and Cryo-Electron Microscopy and Introduction of Structure-Based Metal-Responsive Properties.

The 21-residue peptide α3, which is artificially designed and consists of three repeats of 7 residues, is known to rapidly assemble into the α-helix nanofiber. However, its molecular structure within the fiber has not yet been fully elucidated. Thus, we conducted a thorough investigation of the fiber's molecular structure using solid-state NMR and other techniques. The molecules were found to be primarily composed of the α-helix structure, with some regions near the C- and N-terminal adopting a 310-helix structure. Furthermore, it was discovered that β-sheet hydrogen bonds were formed between the molecules at both ends. These intermolecular interactions caused the molecules to assemble parallelly in the same direction, forming helical fibers. In contrast, we designed two molecules, CaRP2 and βKE, that can form β-sheet intermolecular hydrogen bonds using the entire molecule instead of just the ends. Cryo-EM and other measurements confirmed that the nanofibers formed in a cross β structure, albeit at a slow rate, with the formation times ranging from 1 to 42 days. To create peptide nanofibers that instantaneously respond to changes in the external environment, we designed several molecules (HDM1-3) based on α3 by introducing metal-binding sites. One of these molecules was found to be highly responsive to the addition of metal ions, inducing α-helix formation and simultaneously assembling into nanofibers. The nanofibers lost their structure upon removal of the metal ion. The change occurred promptly and was reversible, demonstrating that the intended level of responsiveness was attained.

Deformation and kerogen macromolecular structure transformations of the Wufeng–Longmaxi shale under the control of the detachment layer

Tectonism caused strong deformation of the organic-rich shale in the detachment layer of the Wufeng–Longmaxi Formation. In this study, the deformation of the samples collected from the detachment layers were observed using an optical microscope and field emission scanning electron microscopy. Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance, X-ray diffraction, and high-resolution transmission electron microscopy were employed to characterize the macromolecular structure of extracted kerogen samples. The research shows that tectonically deformed shale (TDS) is commonly developed in the detachment layer of the Wufeng–Longmaxi Formation, dominated by brittle–ductile and ductile deformation. In the brittle–ductile deformation stage, the aliphatic carbon (fal) decreases, manifested as the decrease of –CH or –CH2 (falH), from 6.77% to 3.12%. The Al/–OX (defined by FTIR A3000–2800/A1800–1520) gradually decreases, indicating that the brittle–ductile deformation has a stronger effect on the aliphatic structure. The aromaticity I and aromatic carbon (fa) show an increasing trend due to aromatization. In the ductile deformation stage, the fal and aliphatic carbon bonded to oxygen increase first and then decrease, falH decreases gradually, and the aliphatic side chain becomes shorter. The Al/–OX shows an increasing trend, and carbonyl decreases from 7.82% to 5.12%, indicating that the effect of ductile deformation on oxygen-containing functional groups is stronger. The fa shows an overall increasing trend, and the aromatic ring carbon and protonated aromatic carbon increase more significantly due to aromatic condensation. The change trend of the interlayer spacing is opposite in these two stages. However, both brittle–ductile and ductile deformation can improve the size and orientation of aromatic fringes to varying degrees, and the latter is more significant. The rigid mineral intrusion and organic matter (OM) chemical structure evolution are the two main reasons for the low development of OM pores in TDS.

The Combined Effect of Nanoclay Powder and Curing Time on the Properties of Class G Cement

When the cement paste is subjected to stresses, the cement matrix and its characteristics are dramatically influenced, especially in the early ages of cement hydration when the cement properties have not yet settled. Nanoclay, which is made up of very small particles, was used to improve the properties of cement. In this study, the early-age performance of cement made with nanoclay powder for use in oil wells is assessed. Ten cement samples were made and cured at varying times (6, 12, 24, 48, and 72 hours), wherein 1% by weight of cement of nanoclay was used in five samples, and in the other five samples, there was no nanoclay present in the cement. Failure properties, petrophysical parameters, and elastic properties were studied for all the cement samples. Nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were all used to describe the cement samples and determine how different curing times affected the cement’s mineralogical and microstructural features. The results displayed that compressive and tensile strengths were shown to increase with curing time for both the base (control) and nanoclay cement samples; however, the compressive and tensile strengths of the nanoclay cement samples were found to be greater than the base sample by 20.2% and 17.9%, respectively. This is due to the presence of more calcium silicate hydrate in these samples. Nanoclay cement had 76.9% lower permeability than control cement, which can be related to the capacity of the nanoclay particles to fill the microstructure dominating the base samples as curing time increased. Young’s modulus of the cement was lowered by 1.8%, while Poisson’s ratio was increased by 2.7% when nanoclay was incorporated. Nanoclay cement has a 29.2% smaller porosity than regular cement, and this porosity increases as the cement cures. The novelty of this work is that several properties of the class G cement were evaluated at the early stage of hydration, where the nanoclay particles were used to improve these properties.

A Diruthenium Metallodrug as a Potent Inhibitor of Amyloid-β Aggregation: Synergism of Mechanisms of Action.

The physical and chemical properties of paddlewheel diruthenium compounds are highly dependent on the nature of the ligands surrounding the bimetallic core. Herein, we compare the ability of two diruthenium compounds, [Ru2Cl(D-p-FPhF)(O2CCH3)3]·H2O (1) (D-p-FPhF- = N,N'-bis(4-fluorophenyl)formamidinate) and K3[Ru2(O2CO)4]·3H2O (2), to act as inhibitors of amyloid aggregation of the Aβ1-42 peptide and its peculiar fragments, Aβ1-16 and Aβ21-40. A wide range of biophysical techniques has been used to determine the inhibition capacity against aggregation and the possible mechanism of action of these compounds (Thioflavin T fluorescence and autofluorescence assays, UV-vis absorption spectroscopy, circular dichroism, nuclear magnetic resonance, mass spectrometry, and electron scanning microscopy). Data show that the most effective inhibitory effect is shown for compound 1. This compound inhibits fiber formation and completely abolishes the cytotoxicity of Aβ1-42. The antiaggregatory capacity of this complex can be explained by a binding mechanism of the dimetallic units to the peptide chain along with π-π interactions between the formamidinate ligand and the aromatic side chains. The results suggest the potential use of paddlewheel diruthenium complexes as neurodrugs and confirm the importance of the steric and charge effects on the properties of diruthenium compounds.

Toward determining amyloid fibril structures using experimental constraints from Raman spectroscopy

We present structural models for three different amyloid fibril polymorphs prepared from amylin20–29 (sequence SNNFGAILSS) and amyloid-β25–35 (Aβ25–35) (sequence GSNKGAIIGLM) peptides. These models are based on the amide C=O bond and Ramachandran ψ-dihedral angle data from Raman spectroscopy, which were used as structural constraints to guide molecular dynamics (MD) simulations. The resulting structural models indicate that the basic structural motif of amylin20–29 and Aβ25–35 fibrils is extended β-strands. Our data indicate that amylin20–29 forms both antiparallel and parallel β-sheet fibril polymorphs, while Aβ25–35 forms a parallel β-sheet fibril structure. Overall, our work lays the foundation for using Raman spectroscopy in conjunction with MD simulations to determine detailed molecular-level structural models of amyloid fibrils in a manner that complements gold-standard techniques, such as solid-state nuclear magnetic resonance and cryogenic electron microscopy.

Grey correlation analysis of macro- and micro-scale properties of aeolian sand concrete under the salt freezing effect

To study the effect of the pore structure of aeolian sand concrete (ASC) with different compositions on its compressive strength in a freeze-thaw environment, ASC with 0% (S0), 25% (S25), 50% (S50), 75% (S75), and 100% (S100) of aeolian sand (AS) content was prepared in our experiment. The damage and degradation laws of the compressive strength of ASC cube in the presence of chloride freeze-thaw were studied, and the compressive strengths of S0, S50 and S100 were predicted from the pore structure parameters. Compressive strength, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) tests of the ASC samples were carried out. Grey correlation analysis was used to analyze the correlation between the pore structure parameters and the compressive strength, and a model was developed to predict the compressive strength of S0, S50 and S100 ASC subjected to freeze-thaw cycles (FTCs). It was shown that ASC with 25% AS content showed a large improvement in compressive strength, which was 6.86% higher than that of the S0 group. With the progression of FTCs, the porosity of ASC increases, and the bound fluid saturation and the proportion of 0–0.1 µm pores decrease. According to the grey correlation analysis, the saturation of bound fluid and the proportion of 0–0.1 µm pores have the strongest correlation with the compressive strength of ASC. The joint prediction model for the compression strength has a correlation coefficient of 0.937, and is able to better predict the compressive strength of ASC at different AS replacement rates during the FTCs.

Bioinspired Folic Acid-ADH-PLGA Polymeric Nanoparticles Loaded with Mangiferin and Piperine: A Promising Strategy for Targeted Delivery in Multidrug-Resistant Lung Cancer Cells

The current study aims to develop mangiferin and piperine dual drug-loaded folic acid-ADH-PLGA polymeric nanoparticles with bioinspired folic acid modifications which were effective carriers for site-specific delivery in multidrug-resistant lung cancer cells. Mangiferin and piperine, two pharmacological agents, were encapsulated within intelligent nanoparticles. These nanoparticles were fabricated utilizing folic acid, poly(lactic-co-glycolic acid) (PLGA), adipic dihydrazide (ADH) and pluronic F-68 as constituent materials. The successful fabrication of these intelligent polymeric nanoparticles was confirmed through comprehensive characterization employing various analytical techniques, including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and atomic force microscopy (AFM). The efficacy of the intelligent polymeric nanoparticles against cancer cells was assessed through the evaluation of several parameters and their effectiveness was established utilizing the MTT assay. Furthermore, a hemolytic toxicity test was performed to ascertain whether the nanoparticles exerted any toxic effects on red blood cells. Mangiferin and piperine loaded FAP-M and FAP-P nanoparticles revealed a remarkable potential for inducing cell death. The findings from in vitro drug release assessments, hemolytic toxicity evaluations, bio-distribution analyses, MTT assays and apoptosis assessments exhibited substantial cell cycle phase arrest akin to the standard control. The comprehensive investigation and findings of the internalization process revealed the enhanced anticancer efficacy of mangiferin and piperine encapsulated in fibroblast activation protein-modified (FAP-M) and FAP-P nanoparticles as well as their biodistribution profile.

Study on the relationship between permeability coefficient and porosity, the confining and osmotic pressure of attapulgite-modified loess

This study investigated attapulgite-modified loess as an efficient and cost-effective method for creating an impermeable liner for landfills in regions with scarce clay resources. Laboratory permeability tests were conducted using a flexible wall permeameter to determine the permeability of compacted loess and attapulgite mixtures under varying osmotic conditions. The relationship between the permeability coefficient, attapulgite dosage, radial pressure, and osmotic pressure was analyzed. Nuclear magnetic resonance and scanning electron microscopy were also used to observe the microstructure of the modified loess. The results showed that attapulgite dosage significantly reduced the permeability coefficient, but the effect became limited when the content surpassed 10%. The decrease of the permeability coefficient of the modified loess is mainly due to the filling of pores between the loess by attapulgite, which makes the pore size and throat size of the modified loess smaller. The modified loess displayed a sheet structure that contributed to an increased permeability coefficient due to increased radial pressure. This study provides valuable insights into using attapulgite-modified loess as a material for landfill lining in regions with scarce clay resources.

Effect of industrial sludge particle size on the performance of baking-free sludge bricks

ABSTRACT Cement solidification is essential to reduce heavy metal leaching from industrial sludge and make it recyclable. This paper studied the effect of aggregate grading optimized by sludge containing heavy metal of different particle sizes on the performance of baking-free sludge bricks, which was mixed with industrial sludge cured by both micro-silica fume and cement. First, the gradation of fine natural aggregates was adjusted according to the Fuller curve. Fine aggregates in baking-free bricks were replaced by artificially processed sludge with particle sizes of 0.15 mm ~0.3 mm and 2.36 mm ~4.75 mm. In this case, a mixed proportion scheme was designed. Then, the strength, water absorption, porosity, and heavy metal leaching were measured. With the help of nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM), the phase and pore structures were observed. The test results showed that: (1) Sludge can replace part of the fine aggregates to make baking-free bricks, resulting in the reduction of the strength of baking-free bricks, but the strength still meets the standard strength requirements of GB/T 21,144-2007. (2) When fine aggregates are partly replaced by sludge with finer particle sizes, baking-free sludge bricks exhibit higher strength, lower water absorption, better pore structures and microphase structure, and stronger solidification of heavy metals, the leaching number of heavy metals meets the standard requirements of GB5085.3–2007, which will be provided support for actual industrial production. Implications: Cement solidification is an essential means to reduce the heavy metal leaching from industrial sludge and make it recyclable. This paper studied sludge containing heavy metal of different particle sizes on the performance of baking-free sludge bricks. This paper analyzed the compressive strength, porosity and water absorption of baking-free bricks mixed with sludge of different partical sizes, and adopted the NMR to characterize the pores of baking-free bricks, and the SEM to observe the baking-free bricks resultants and the interfacial transition zone (ITZ). The heavy metal leaching test verified the environmental benefits of baking-free bricks mixed with sludge instead of aggregates. There not only make full use of solid wastes, but also thus minimizing pollution to the environment, which provide support for actual industrial production and a reference for studying industrial sludge recycling technology.

One-Dimensional Compressibility and Creep Characteristics of Unsaturated Compacted Loess Based on Incremental Loading and Constant Rate of Strain Methods

In engineering practice, unsaturated compacted loess is often utilized as a filling material in the loess regions. The loess inevitably undergoes one-dimensional compressibility and creep deformation due to the long-term effects of the upper soil layers and buildings. When the deformation is large enough, it tends to damage buildings and threaten engineering safety. In this regard, the one-dimensional compressibility and creep properties of unsaturated compacted loess based on incremental loading (IL) and constant rate of strain (CRS) methods have been studied. First, soil materials with an initial moisture content of 15% were prepared and then compacted into soil samples with an 80 mm diameter and a 10 mm height. Second, the compressibility and creep properties of the compacted loess samples obtained via the IL and CRS compression tests were compared and analyzed. In this study, several parameters, including the primary compression index Cc and secondary compression index Cα, were derived. Meanwhile, the moisture content of the samples was measured via electrical resistivity methods. Finally, the microstructural characteristics were derived via nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) tests. The results showed that Cc and Cα increased with the increase in moisture content and vertical stress; Cα/Cc ranged from 0.026 to 0.042. Compared with the compression parameters and deformation of the samples, those obtained via the CRS tests are a little larger than those obtained via the IL tests for a given loading and initial moisture content. The electrical resistivity depends on pore water-connected channels, which were deeply affected by the initial moisture content, vertical stress and loading duration (or strain rate). Moreover, as vertical stress increased, the pore size and pore area gradually decreased, the coarse particles were broken, and the fine particles increased. The contacts between particles changed from point-to-point contacts and edge-to-edge contacts to face-to-face contacts. Meanwhile, as vertical stress and loading rate increased, the loess particles were apt to vary from irregular elongated particles to equiaxial circular particles. This investigation can provide a theoretical base and experimental support for improving ground stability and preventing landslide disasters in loess regions.

Investigation of cross-scale characterization of porous structure and fluid index in bituminous coal via microwave-LN2 freeze-thaw cycles

Microwave-LN2 cyclic processing (MLCP) is a clean and high-efficiency anhydrous fracturing technology. The change in the porous structure of coal after freeze-thaw cycles significantly affects development efficiency of coalbed methane (CBM) in low porosity and permeability reservoirs, while there is a lack of in-depth macro-meso-micro studies. The damage mechanism of coal under microwave-LN2 cold and thermal shock and the evolution of pore fluid reservoir space is based on cross-scale pore characterisation. This paper evaluates the multi-scale porous structure variations of coal before and after MLCP was assessed by hydrogen nuclear magnetic resonance (1H NNR) and field emission scanning electron microscopy (FE-SEM). The evolutionary trends in coal pore fluid fugacity space under freeze-thaw cycles was indirectly characterised by T1-T2 spectra. Additionally, utilizing T2 distribution, peak area and pore throat changes reflect the evolution trend of coal pore space. The results indicate that as the cycles increased, the coal free water and total fluid reservoir space gradually expanded beyond the cycle threshold (n > 10), the free-fluid index rose to 25.68 %, and the free fluid saturation increased by 20.39 %. Additionally, the NMR permeability of the coal increased by 98.37–1471.65 %, and the pore throat distribution increased by 28.05 %. Comprehensive analysis showed that as the cycles progressed, the free water space in the pore space increased significantly, the proportion of bound water gradually decreased, and the internal pores and fluid space of the coal were improved. This study provides fundamental support for multidimensional evaluation of the porous structure of microwave-LN2 freeze-thaw cycles.

Fibrils Emerging from Droplets: Molecular Guiding Principles behind Phase Transitions of a Short Peptide-Based Condensate Studied by Solid-State NMR.

Biochemical reactions occurring in highly crowded cellular environments require different means of control to ensure productivity and specificity. Compartmentalization of reagents by liquid-liquid phase separation is one of these means. However, extremely high local protein concentrations of up to 400 mg/ml can result in pathological aggregation into fibrillar amyloid structures, a phenomenon that has been linked to various neurodegenerative diseases. Despite its relevance, the process of liquid-to-solid transition inside condensates is still not well understood at the molecular level. We thus herein use small peptide derivatives that can undergo both liquid-liquid and subsequent liquid-to-solid phase transition as model systems to study both processes. Using solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM), we compare the structure of condensed states of leucine, tryptophan and phenylalanine containing derivatives, distinguishing between liquid-like condensates, amorphous aggregates and fibrils, respectively. A structural model for the fibrils formed by the phenylalanine derivative was obtained by an NMR-based structure calculation. The fibrils are stabilised by hydrogen bonds and side-chain π-π interactions, which are likely much less pronounced or absent in the liquid and amorphous state. Such noncovalent interactions are equally important for the liquid-to-solid transition of proteins, particularly those related to neurodegenerative diseases.